1. Field of the Invention
The present invention relates to a method for removing conductive portions formed on surfaces of dielectric resonators used in oscillators, filters, duplexers, etc., and on surfaces of dielectric substrates.
2. Description of the Related Art
FIG. 4 shows a dielectric resonator for use in an oscillator or a filter. A dielectric resonator 10 is formed of a rectangular prism-shaped dielectric 11 having a through-hole 12, an outer conductor 13 formed on the external surfaces thereof except for one end in which the through-hole 12 is formed, an inner conductor 14 formed on the inner peripheral surface of the through-hole 12, an input-output electrode 15 formed in the vicinity of an open end in which a conductive portion is not formed, and a connecting conductor 16 which connects the input-output electrode 15 to the inner conductor 14. As a method for forming a dielectric resonator having the above-mentioned structure, there is a method in which a predetermined portion of conductive portions are removed after forming of the conductive portions by copper plating, for example, on the entirety of the surfaces of a rectangular prism-shaped dielectric having a through-hole.
Furthermore, as a specific method for removing conductive portions of a dielectric resonator, a removing method using a laser is effective because the removal can be precisely achieved for arbitrary shapes using a polarizing mirror which is not in contact with the dielectric resonator. A characteristic adjustment such as a frequency adjustment can also be achieved by removing a portion of conductive portions by a laser.
Referring to a process diagram shown in FIG. 5, a conventional method for removing conductive portions will now be described.
As a first process, a predetermined portion of conductive portions is removed using a YAG laser. When a conductive portion is removed using a laser such as a YAG laser, a dielectric and a conductive portion fused by intense heat of the laser are solidified and the electric resistance thereof is decreased so that affected layers are produced, and the dielectric is rapidly quenched from a high temperature so as to be reduced by oxygen deficiency so that semi-conductive affected layers are produced. When such an affected layer is produced, no-load xe2x80x9cQxe2x80x9d (referred as xe2x80x9cQoxe2x80x9d below) of the dielectric resonator is deteriorated. Accordingly, in a second process, the affected layer, having decreased electric resistance, is etched using dilute sulfuric acid so that the deteriorated xe2x80x9cQoxe2x80x9d is improved.
As a third process, the semi-conductive affected layer due to a reducing reaction is re-oxidized by a heat-treatment in air atmosphere. Since the conductive portion, which is not essentially to be oxidized, is oxidized in the third process, an oxidized conductive portion is etched using dilute sulfuric acid in a fourth process. By being subjected to these processes, the dielectric resonator 10 shown in FIG. 4 can be obtained.
In a conventional method for removing conductive portions, utilization of the first to fourth processes is required, so that the number of manufacturing steps is increased. Removing the conductive portion by a laser in the first process, etching by dilute sulfuric acid in the second and fourth processes, and heat treating for re-oxidizing the semi-conductive affected layer due to a reducing reaction in the third process must be performed, using different equipment, resulting in reduced productivity.
To overcome the above described problems, preferred embodiments of the present invention provide a method for removing conductive portions, which does not require a large number of pieces of equipment, and which does not cause deterioration of the xe2x80x9cQoxe2x80x9d of a dielectric resonator, etc., by solving those problems.
One preferred embodiment of the present invention provides a method for removing conductive portions, comprising the steps of: a first process for removing a conductive portion formed on a dielectric using a laser; and a second process for removing an affected layer produced in the removed portion by the laser using a short pulse laser.
A short pulse laser has an extremely short pulse duration and is thereby able to remove the affected layer without thermal load. That is, the affected layer can be removed without using a large number of apparatuses, so that a dielectric resonator with a non-deteriorated xe2x80x9cQoxe2x80x9d, etc., can be easily produced.
In the above described method, the laser used in the first process may be a harmonic YAG laser.
When a harmonic YAG laser, such as a second harmonic YAG laser having double the frequency and one-half the wavelength, and a fourth harmonic YAG laser having four times the frequency and one-quarter the wavelength are used, the accuracy is improved due to a reduced wavelength, and the thermal load is also reduced.
In the above described method, the laser used in the first process may be a second harmonic YAG laser.
When a second harmonic YAG laser among harmonic YAG lasers is used, an appropriate output-power can be obtained while maintaining sufficient accuracy.
In the above described method, the short pulse laser used in the second process may be a YAG short pulse laser.
Among short pulse lasers, the YAG short pulse laser achieves high amplification gain utilizing a crystalline solid so as to have features of high oscillating output-power, stable performance, etc., resulting in increased productivity.
In the above described method, a gas including oxygen may be supplied to the removing conductive portion in the first process.
Thereby, the semi-conductive dielectric reduced by oxygen deficiency can be reduced so that the portion removed by the short pulse laser is reduced, resulting in further increased productivity.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.